Ceramic materials have been present in the history of man for many different purposes, from purely decorative applications, to more advanced applications such as structural components. Previously, ceramics was considered as the art of cooked earths, however nowadays involves more complex topics in the field of materials science far exceeding the limits of traditional ceramics.
Specific case are the ceramics used in the manufacture of electrical components. Historically and traditionally, porcelain has been the base ceramic material used to manufacture these products, due to the inherent properties it presents, besides other processing aspects and even for economic reasons. Some of the features that have gave porcelain high value in the electricity industry are: excellent dielectric and mechanical performance, except for the impact, a vitrified structure that resists water absorption, refractory qualities, resistance to oils, vapors, etc., attractive appearance, ease of shaping into different shapes, besides being relatively inexpensive. Coupled with this, the porcelains have advantages over other organic type insulating materials in terms of chemical stability and durability when exposed to high temperatures, damp or contaminated media, besides not undergoing degradation from UV radiation action.
Porcelain for electrical insulators has evolved through history, from the components used as raw materials and their manufacturing processes to optimization of microstructural aspects for specific characteristics in the final product. The siliceous electrotechnical porcelains belong to the triaxial ceramic quartz-clay-feldspar system and develop their characteristic properties to achieve a high degree of vitrification in their microstructure, which occurs after the heat sintering process at temperatures of about 1250° C. Typically, the final microstructure of electric porcelain consists of quartz (SiO2) and mullite (3Al2O3.2SiO2) crystals embedded in an amorphous or glassy matrix, as well as the presence of closed porosity.
Triaxial electrical grade porcelain used in this type of insulators in addition to complying with a suitable dielectric behavior, is also essential to present a good mechanical performance when in operation. There are several types of porcelain pastes used to make porcelain electrical insulators, among which triaxial siliceous type paste (C110) and triaxial aluminous type paste (C120), designated by the IEC standard (International Electrotechnical Commission) 60672-1 (Ceramic and glass insulating materials—Part 1: Definitions and classification) are highlighted, which are most commonly used for this specific application. Aluminous pastes have higher mechanical strength values, however they are more expensive than silica based porcelains, because of the alumina concentrations which is used as raw material, and other process aspects, such as higher firing temperatures and increased machinery wear.
It is very important that the porcelain used in electrical insulators have suitable mechanical and insulation properties, so as to ensure product reliability when in operation. In recent years, several researches have been developed to increase the mechanical strength of the electrical porcelains, the most searched fields being strengthening of the porcelain matrix by microstructural modification, the addition of different types of macro-ceramic particles, and the development and application of new enamel formulations.
Recently, with the advent of nanoscience and nanotechnology, new alternative solutions are presented to improve the characteristics and performance of materials in general. In the case of ceramic materials, concepts have been verified based on the use of small additions of nanoscale particles for improving various properties such as mechanical strength, wear resistance, chemical resistance, among other. These studies demonstrate that nanoparticles significantly contribute to the final characteristics of ceramics.
However, the incorporation of nanosized ceramic oxides, has virtually not been considered in reinforcing siliceous porcelain systems, specifically those electrical grade with application in insulators, which represents an alternative to improve the characteristics of electrotechnical porcelains, so as to obtain products with high added value, high reliability and better performance when in operation.
Thus, this invention has as its fundamental objective the development of a porcelain paste nanostructured through the concept of incorporating ceramic oxides at nano-metric level in specific concentrations, having mechanical and dielectric features superior to those of a conventional silica-based electrical porcelain with application in electrical components, such as electrical insulators.